The present invention relates to extrusion heads for producing yarns from a thermoplastic material which is heated to form a paste, of the type comprising at least one body defining a pasty material distribution chamber above a horizontal plate perforated with extrusion apertures, the chamber being supplied with pasty material via at least one upper side feed duct extended about an axis in its terminal section connecting with the chamber.
A particularly important, although not exclusive, application of the invention is in the field of the manufacture of synthetic yarns from molten polymer.
Extrusion heads for producing synthetic yarns are already known. They comprise a body having a distribution zone for the pasty material and an extrusion chamber provided at its base with a spinning plate perforated with holes from which continuous filaments are formed. These filaments are gathered together so as to produce one or a more yarns.
The holes provided in the spinning plate can be distributed over a rectangular, triangular or annular surface.
In general the known extrusion heads further comprise a central molten polymer feed duct disposed along the axis of the extrusion head and of the yarn(s) produced.
In this type of extrusion head it is difficult, or even impossible, to introduce a central filiform component or core into the bundle of extruded synthetic filaments.
An extrusion head is also known (U.S. Pat. No. 3,307,216) which allows a body to be introduced into the bundle of filaments produced. A head of this type comprises a cylindrical body defining an annular chamber for distributing the pasty material above a perforated plate. The chamber is supplied with pasty material via an upper lateral feed duct. The body comprises a central cylindrical recess into which it is possible to introduce a component which is to be incorporated in the bundle of filaments which surround the latter after extrusion.
However, a head of this type is not without disadvantages either.
Irrespective of the path which the product takes between the introduction channel and the plate, this type of head does not allow for the presence of a pasty product of homogeneous viscosity at the plate perforated with holes through which the extruded filaments emerge, so creating differences in quality and durability in the filaments of extruded material produced.